[Info-vax] SET TERM /TTSYNC on ancient VMS versions

[Chris]

On 08/16/18 18:45, Jan-Erik Söderholm wrote:

> Didn't the setup screens had a "flow control" option that on many
> terminals could be set to "soft", "hard" or "none"?
> "Soft" was Xon/Xoff, hard was the "modem lines" (I remember it as
> CTS/CTR or similar but doesn't matter) and "none" was, well, none...

That sounds familiar. The last VT terminals I used were 300 series,
but i'm pretty sure the 220 had it as well, which dates it back to
the mid eighties or even earlier.

>
> And yes, as the name implies, the modem control lines might originally
> have been meant for modem control, but they works just as well for flow
> control, if you want to.
>

Common in industry, which still uses a lot of serial line
hardware. A common pair being rts / cts, to limit data rates from
host to a peripheral. RS232 only over short distances, the 423 / 485
differential for greater distances.

The early uart devices, also used by dec, had no buffering, so
as soon as a char arrived, you got an interrupt or had to use a polling
loop. Later devices had multibyte buffering, so you had a bit more
time to read the byte and decide what to do with it, important at the
higher baud rates. The later dec serial cards used custom
microcircuits and no idea what they had on chip, but probably used dma
by then...

Chris